Conventionally, a control unit which performs an automatic-stop control in which the operation (rotation) of an engine is automatically stopped when a predetermined automatic-stop condition is satisfied, for the purpose of improvement of fuel consumption in a vehicle carrying the engine and reduction of the quantity of exhaust gas discharged from the vehicle, etc. has been known.
Such a control unit automatically restarts the engine, when a restart demand of the engine occurs as in a case where an accelerator operation is made or a brake operation is released. In this case, the control unit performs either one of (1) usual control, (2) ignition start-up control, and (3) starter start-up control, depending on the engine rotational speed at the time of the occurrence of the restart demand, to restart the engine, for instance.
By the way, the ignition start-up control is performed when the engine rotational speed has fallen to a level in which it is difficult to restart the engine by the usual control (a fuel injection and an ignition in a compression stroke) although the engine rotational speed has not yet reached “0” completely. In accordance with the ignition start-up control, a fuel injection and an ignition are performed in a cylinder in an expansion stroke (hereafter, may be referred to as an “expansion stroke cylinder”) so that a cylinder in a compression stroke (hereinafter, may be referred to as a “compression stroke cylinder”) can get over the top dead center of the cylinder. Furthermore, in the ignition start-up control, a fuel injection and an ignition in this expansion stroke cylinder are carried out at least once or more, and, in addition to the above, fuel injection is performed one by one also to a compression stroke cylinder so that the rotational speed of the engine goes up promptly, and electrification to an igniter is started in order to perform an ignition after the cylinder reaches the compression top dead center.
By the way, in the ignition start-up control, there is a possibility that the compression stroke cylinder cannot get over the top dead center of the cylinder and thereby the engine may begin a negative rotation (inverse rotation) even though a fuel injection and an ignition in the expansion stroke cylinder are performed. Namely, a start-up failure may occur. In this case, when an interception of the electrification to an igniter is performed in the compression stroke cylinder in which a fuel injection has been already made, there is a possibility that fuel may burn to promote the negative rotation of the engine although the cylinder is still in a compression stroke. Then, one of conventional controllers is configured to postpone an execution of an ignition in the compression stroke cylinder in which fuel injection has been already performed as well as to drive a starter, and to perform an ignition at a time point when the compression stroke cylinder get over the compression top dead center and results in an expansion stroke, in a case where the engine begins a negative rotation (for instance, refer to Japanese Patent No. 5,456,088 (JP 5,456,088 B2)).